1. Field of the Invention
The present invention relates to a spin-valve thin-film magnetic element which undergoes a change in electrical resistance in relation to the magnetization vector of a pinned magnetic layer and the magnetization vector of a free magnetic layer affected by an external magnetic field, and to a thin-film magnetic head provided with the spin-valve thin-film magnetic element. In particular, the present invention relates to a technology suitable for a spin-valve thin-film magnetic element which includes a free magnetic layer having improved soft magnetic characteristics and thus exhibits an enhanced rate of change in resistance.
2. Description of the Related Art
A spin-valve thin-film magnetic element is a type of giant magnetoresistive element (GMR) exhibiting a giant magnetoresistive effect and detects recorded magnetic fields from a recording medium such as a hard disk. Among GMRs, the spin-valve thin-film magnetic element has a relatively simple structure, and exhibits a high rate of change in resistance in response to external magnetic fields and thus a change in resistance in a weak magnetic field.
Each of FIGS. 24 to 26 is a cross-sectional view of an exemplary conventional spin-valve thin-film magnetic element when viewed from a face opposing the recording medium (air bearing surface: ABS).
A shielding layer is provided on or under the spin-valve thin-film magnetic element, separated by a gap layer, so as to constitute a GMR read head comprising the spin-valve thin-film magnetic element, the gap layer, and the shield layer. An inductive write head may be deposited on the GMR read head.
This GMR head is installed at the trailing end face of a floating slider together with the inductive head so as to constitute a thin-film magnetic head for detecting recorded magnetic fields written on a magnetic recording medium such as a hard disk.
The conventional spin-valve thin-film magnetic element shown in FIG. 24 is known as a bottom-type hard-bias single spin-valve thin-film magnetic element. The spin-valve thin-film magnetic element comprises a composite of an antiferromagnetic layer 122, a pinned magnetic layer 123, a nonmagnetic conductive layer 124, and a free magnetic layer 125. The composite is provided with a pair of hard bias layers on two sides of the composite.
In this spin-valve thin-film magnetic element, the magnetic recording medium, typically a hard disk, moves in the Z direction in the drawing and a leakage magnetic field occurs in the Y direction in the drawing.
The conventional spin-valve thin-film magnetic element shown in FIG. 24 includes: a composite 120 comprising, an underlayer 121 at the bottom, the antiferromagnetic layer 122, the pinned magnetic layer 123, the nonmagnetic conductive layer 124, the free magnetic layer 125, and a protective layer 127; a pair of hard bias layers (permanent magnet layers) 129 formed on two sides of the composite 120; and a pair of electrode layers 128 formed on the hard bias layers. Generally, the antiferromagnetic layer 122 is composed of an Fe—Mn alloy or a Ni—Mn alloy, the pinned magnetic layer 123 and the free magnetic layer 125 are composed of a Ni—Fe alloy, the nonmagnetic conductive layer 124 is composed of a Co—Pt alloy, the hard bias layers 129 are composed of a Co—Pt alloy, and the electrode layers 128 are composed of Cr or W. The underlayer 121 and the protective layer 127 are composed of Ta or the like.
The magnetic-recording track-width Tw is mainly determined by the width of the upper surface of the composite 120.
As shown in FIG. 24, the exchange anisotropic magnetic field generated by exchange coupling at the interface with the antiferromagnetic layer 122 puts the pinned magnetic layer 123 into a single-magnetic-domain state in the Y direction (the direction of the leakage magnetic field from the recording medium, i.e., the height direction). The free magnetic layer 125 is affected by a bias magnetic field from the hard bias layers 129 and orients in the direction opposite to the X1 direction.
In other words, the magnetization vector of the pinned magnetic layer 123 and that of the free magnetic layer 125 are set to be orthogonal to each other.
In this spin-valve thin-film magnetic element, the electrode layers 128 formed on the hard bias layers 129 supply a detecting current (sensing current) to the pinned magnetic layer 123, the nonmagnetic conductive layer 124, and the free magnetic layer 125. There is a leakage magnetic field vector from the magnetic recording medium. When the magnetization vector of the free magnetic layer 125 changes from the direction opposite to the X1 direction to the Y direction, the electrical resistance is changed in relation to the pinned magnetization vector of the pinned magnetic layer 123 and the change in the magnetization vector of the free magnetic layer 125 (this change is known as the “magnetoresistive (MR) effect”). As a result, the leakage magnetic field from the magnetic recording medium is detected as a change in voltage due to the change in the electrical resistance.
The spin-valve thin-film magnetic element shown in FIG. 25 is also a bottom-type element having an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic conductive layer, and a free magnetic layer, as is the spin-valve thin-film magnetic element shown in FIG. 24, but differs in that it is a side exchange bias type single spin-valve thin-film magnetic element.
In this spin-valve thin-film magnetic element, a magnetic recording medium such as a hard disk moves in the Z direction in the drawing and the vector of the leakage magnetic fields from the recording medium is in the Y direction in the drawing.
In FIG. 25, symbol K denotes a substrate. The antiferromagnetic layer 122 is formed on the substrate K. A pinned magnetic layer 123 is formed on an antiferromagnetic layer 122, a nonmagnetic conductive layer 124 is formed on the pinned magnetic layer 123, and a free magnetic layer 125 is formed on the nonmagnetic conductive layer 124. A pair of bias layers 126 are formed on the free magnetic layer 125 with a gap equal to the magnetic recording track width Tw between the bias layers 126. A pair of electrode layers 128 are formed on the bias layers 126.
The antiferromagnetic layer 122 is formed of a NiO alloy, an FeMn alloy, a NiMn alloy, or the like. The pinned magnetic layer 123 and the free magnetic layer 125 are formed of elemental Co, a NiFe alloy, or the like. The nonmagnetic conductive layer 124 is a Cu layer. The bias layers 126 are composed of an antiferromagnetic material having a disordered face-centered cubic crystalline structure such as an FeMn alloy. The electrode layers 128 are formed of Cu, Au, Cr, W, Ta, or the like.
As shown in FIG. 25, the pinned magnetic layer 123 is magnetized by the exchange anisotropic magnetic field generated by an exchange coupling at the interface with the antiferromagnetic layer 122. The magnetization vector of the pinned magnetic layer 123 is pinned in the Y direction in the drawing, i.e., the direction away from the recording medium (the height direction). The exchange anisotropic magnetic field generated by the bias layer 126 puts the free magnetic layer 125 into a single-magnetic-domain state. The magnetic vector of the free magnetic layer 125 is set in the direction opposite to the X1 direction, in other words, in the direction substantially orthogonal to the magnetization vector of the pinned magnetic layer 123.
In this spin-valve thin-film magnetic element, the electrode layers 128 supply a sensing current to the free magnetic layer 125, the nonmagnetic conductive layer 124, the pinned magnetic layer 123, and the vicinity thereof. When there is a leakage magnetic field in the Y direction in the drawing from the magnetic recording medium moving in the Z direction, the magnetization vector of the free magnetic layer 125 changes from the direction opposite to the X1 direction to the Y direction in the drawing. Such a change in the magnetization vector of the free magnetic layer 125 causes the electrical resistance to change in relation with the magnetization vector of the pinned magnetic layer 123; consequently, the leakage magnetic field from the magnetic recording medium is detected as a change in voltage due to the change in the electrical resistance.
The conventional spin-valve thin-film magnetic element shown in FIG. 26 is a bottom-type exchange bias single spin-valve thin-film magnetic element comprising a composite of a antiferromagnetic layer 122, a pinned magnetic layer 123, a nonmagnetic conductive layer 124, a free magnetic layer 125, and an exchange bias layer 126.
In this spin-valve thin-film magnetic element, a magnetic recording medium such as a hard disk moves in the Z direction in the drawing and the vector of the leakage magnetic field from the magnetic recording medium is in the Y direction.
The spin-valve thin-film magnetic element shown in FIG. 26 includes: a composite 120 comprising an underlayer 121 at the bottom, an antiferromagnetic layer 122, a pinned magnetic layer 123, a nonmagnetic conductive layer 124, a free magnetic layer 125, an exchange bias layer 126, and a protective layer 127; and a pair of electrode layers 128 formed on two sides of the deposit 120. Generally, the antiferromagnetic layer 122 is composed of a Ni—Mn alloy or the like, the pinned magnetic layer 123 and the free magnetic layer 125 are composed of a Ni—Fe alloy or the like, the nonmagnetic conductive layer 124 is composed of Cu, the bias layer 126 is composed of an Fe—Mn, and the electrode layers 128 are composed of a Cr or W. The underlayer 121 and the protective layer 127 are formed of Ta or the like.
It should be noted that the magnetic recording track width Tw is determined by the width of the upper surface of the composite 120.
As shown in FIG. 26, the exchange anisotropic magnetic field generated by the exchange coupling at the interface with the antiferromagnetic layer 122 puts the pinned magnetic layer 123 into a single magnetic domain state in the Y direction (the direction of the leakage magnetic field from the recording medium, i.e., the height direction). The magnetization vector of the free magnetic layer 125 is oriented in the direction opposite to the X1 direction due to the exchange anisotropic magnetic field generated by the exchange coupling at the interface with the exchange bias layer 126.
In other words, the magnetization vector of the pinned magnetic layer 123 and that of the free magnetic layer 125 are set to be orthogonal to each other.
In this spin-valve thin-film magnetic element, the electrode layers 128 supply a detecting current (sensing current) to the free magnetic layer 125, the nonmagnetic conductive layer 124, the pinned magnetic layer 123, and the vicinity thereof. There is a leakage magnetic field vector from the recording medium. When the magnetization vector is changed from the direction opposite to the X1 direction to the Y direction, the electrical resistance changes in relation to the pinned magnetization vector of the pinned magnetic layer 123, and the leakage magnetic field from the recording medium is detected as a change in voltage due to the change in the electrical resistance.
There is a constant demand for higher recording density in the field of recording media such as hard disks. In order to improve the recording density, the magnetic recording track width must be made narrower. There is a growing demand for a narrower track and improved detection sensitivity.
In the hard-bias spin-valve thin-film magnetic element shown in FIG. 24, the free magnetic layer 125 has, at each side, a region easily pinned by the strong magnetic field from the hard bias layers 129. In such a region, the magnetization vector is hampered from changing in response to the external magnetic field; consequently, as shown in FIG. 24, an insensitive region with degraded sensitivity is generated at each side.
Accordingly, the center region of the composite 120 excluding the insensitive regions is a sensitive region which exhibits the GMR effect and is the only region fully responsible for reading the recording medium. The width of the sensitive region is smaller than the initial magnetic recording track width Tw by a length equivalent to the total width of the insensitive regions. Since the width of the insensitive region varies, it is difficult to precisely define the effective magnetic recording track width. When the initial magnetic recording track width Tw is set smaller, the rate of change in resistance (ΔR/R) in the GMR effect decreases, resulting in degradation of the detection sensitivity. With the degraded detection sensitivity, it is difficult to improve the recording density.
In the side exchange bias spin-valve thin-film magnetic element shown in FIG. 25, the magnetization vector of the free magnetic layer 125 is substantially orthogonal to the magnetization vector of the pinned magnetic layer 123 due to the exchange coupling to the bias layer 126 composed of an antiferromagnetic material.
The side exchange bias spin-valve thin-film magnetic element is more suitable for accommodating a higher recording density and a narrower magnetic recording track width Tw compared to the hard bias spin-valve thin-film magnetic element in which the effective magnetic recording track width is difficult to control due to the presence of the insensitive regions.
However, in the spin-valve thin-film magnetic element shown in FIG. 25, the thickness of the bias layer 126 decreases at sloped peripheries 126s of the track. Thus, the effect generated by the exchange coupling between the free magnetic layer 125 and the bias layer 126 is decreased at the sloped peripheries 126s of the track. Consequently, magnetic resistance in the free magnetic layer 125 undesirably changes at lateral portions 125s of the track in response to the external magnetic field even though the lateral portions 125s are insensitive regions, thus outputting undesired signals relative to the read output of the sensitive region.
This is especially problematic because, since the width and the intervals of the recording tracks on the magnetic recording medium are decreased to achieve higher recording density, the lateral portions 125s may read-out the information on the adjacent track relative to the magnetic recording track which the sensitive region should have had read. This problem of side—reading may generate noise in the output signals, causing errors.
Thus, the effective track width cannot be controlled precisely, and the detection precision is degraded. This is problematic especially in spin-valve thin-film magnetic elements designed for use with magnetic recording track width of 0.5 μm or less.
Also, when the effect of the exchange coupling between the free magnetic layer 125 and the bias layer 126 is decreased at the sloped peripheries 126s, the magnetization vector at the center portion of the sensitive region in the free magnetic layer 125 becomes significantly different from the magnetization vector in the sloped peripheries 125s. Such a difference in the free magnetic layer 125 may inhibit the free magnetic layer 125 from being in a single-magnetic-domain state as if there is a magnetic wall inside, the magnetization vectors become non-uniform, and Barkhausen noise may be generated causing instability and errors in processing the signals provided from the magnetic recording medium.
In the exchange bias spin-valve thin-film magnetic element shown in FIG. 26, unlike the side exchange bias type shown in FIG. 25, the sensitive region of the free magnetic layer 125 is directly connected to the exchange bias layer 126. In this configuration, the exchange anisotropic magnetic field generated by the exchange coupling at the interface between the free magnetic layer 125 and the exchange bias layer 126 becomes excessively strong, tightly pinning the magnetization vector of the free magnetic layer 125. Accordingly, when the external magnetic field is applied for detection, the magnetization vector of the free magnetic layer 125 cannot rotate and change, precluding a change in the resistance of the sensing current and thereby degrading the detection sensitivity.
Furthermore, when manufacturing the side exchange bias type spin-valve thin-film magnetic element shown in FIG. 25 and the exchange bias type spin-valve thin-film magnetic element shown in FIG. 26, (a) a step of annealing in a first magnetic field so as to set the magnetization vector of the antiferromagnetic layer 122 in the Y direction and (b) a step of annealing in a second magnetic field so as to set the magnetization vector of the free magnetic layer 125 in a direction opposite to the X1 direction must be successively performed. However, during the step (a), the exchange anisotropic magnetic field acting at the interface between the antiferromagnetic layer 122 and the pinned magnetic layer 123 rotates from the Y direction to the direction opposite to the X1 direction. As a result, the magnetization vector of the pinned magnetic layer 123 and that of the free magnetic layer 125 are no longer orthogonal to each other and the degree to which the output waveform is out of symmetry (asymmetry) may be increased.
Here, the asymmetry of the output depends on the relationship between the magnetization vector of the pinned magnetic layer 123 and that of the free magnetic layer 125. In the spin-valve thin-film magnetic element, the smaller the asymmetry of the output, the better. An increase in asymmetry causes degradation in the output characteristics of the spin-valve thin-film magnetic element.
It should be noted that the present inventors have disclosed a configuration regarding the exchange bias spin-valve thin-film magnetic element shown in FIG. 26 in Japanese Unexamined Patent Application Publication No. 10-294506 and a configuration regarding the side exchange bias spin-valve thin-film magnetic element shown in FIG. 25 in Japanese Patent Application No. 11-157132 prior to this application. However, these configurations also suffer from the above-described problems.